Too much fructose may raise blood pressure

NEW YORK (Reuters Health) - A diet high in the sugar fructose raises blood pressure in men, while a drug used to treat gout seems to protect against the blood pressure increase.

That' according to study findings presented Wednesday at the American Heart Association's High Blood Pressure Research Conference.

"This is the first study to show that fructose can raise blood pressure in humans," study chief Dr. Richard Johnson, from the University of Colorado, Aurora, told Reuters Health.

A sweetener known as high-fructose corn syrup has been widely used in sodas and processed foods since the 1980s, and some researchers have blamed this trend at least in part for the concurrent rise in obesity and diabetes.

In his study, Johnson said that it was "remarkable" how quickly people with high fructose diets developed increased blood pressure and other features of the so-called metabolic syndrome -- a cluster of risk factors for heart disease and type 2 diabetes.

"The good news is that we were able to reverse this with dietary counseling and implementation of a low fructose diet after the study," Johnson said.

In addition, the gout drug allopurinol seemed to halt the blood pressure increase, most likely by lowering uric acid, which affects blood pressure. Fructose is the only common sugar known to increase uric acid levels.

The study involved 74 adult men, average age 51, who consumed 200 grams of fructose per day in addition to their regular diet. The amount of fructose is much higher than the estimated US daily intake of 50 to 70 grams of fructose consumed by most US adults. Half of the men were randomly assigned to get the gout drug allopurinol and the other half acted as controls.

After just 2 weeks on the diet, the high-fructose minus allopurinol group experienced significant average blood pressure increases of about 6 millimeters of mercury (mm Hg) in systolic blood pressure (the pressure when the heart beats) and about a 3 mm Hg rise in diastolic blood pressure (the pressure between heartbeats).

On the other hand, men on the high-fructose diet plus allopurinol saw virtually no increase in systolic blood pressure. The blood pressure levels of most of the men in the study returned to normal within 2 months of the study's conclusion when the men returned to their normal dietary intake.

In addition, after just 2 weeks, the incidence of metabolic syndrome more than doubled in the men who consumed a fructose-rich diet minus allopurinol. Among men consuming fructose plus allopurinol, virtually no change in the rate of metabolic syndrome occurred, perhaps because the gout drug prevented the blood pressure rise associated with increased fructose intake.

"These results suggest that fructose may be a cause of metabolic syndrome," Johnson said in a prepared statement. In addition to high blood pressure, features of the metabolic syndrome include fat accumulation around the waist, low levels of "good" HDL cholesterol, high levels of harmful blood fats called triglycerides, and high blood sugar.

Fruit, which has just 4 to 10 grams of fructose per serving, also contains many healthful substances including antioxidants, vitamin C, potassium and fiber, Johnson added. The main risk for excessive fructose intake in the Western diet comes from sweetened drinks and foods rich in sugar or high fructose corn syrup, he noted.